GPS
In these last few weeks, Europe has finally agreed to development modules in its civilian satellite voice navigation system Galileo, launching their second test satellite so that they can validate technical aspects before starting on the implementation of a constellation of 30 satellites, providing them with freedom from the GPS system operated by the Pentagon. The commercial phase should now be able to commence in 2013, five years behind its original schedule, a period in which other nations have developed their own GNSS (Global Navigation Satellite System). Let’s take a look at the goals of Europe and the challenges that are not only technical and strategic, but also political.
The Galileo project is a second generation GNSS (Global Navigation Satellite System - with the American GPS and Russian Glonass systems being first generation) operating in the L1, L2 and L5 frequency ranges (bands that verify the systems integrity) so as to assure the functions and positioning of the satellite for a multitude of applications.
On principle it will be based on a constellation of 30 satellites and a network of ground stations. The satellites will emit precise information about time measurements towards the ground thanks to their onboard atomic clocks.
Galileo will be distinguished from the GPS system on a number of essential points:
- It will improve the precision of you position to 1 meter, against 5 to 10 meters for GPS
- It will offer a superior signal reliability thanks to a specific emission channel (integrity message) informing eventual dysfunctions and a guarantee of working from all points on the globe
- Used for civil use, with it not being disrupted for geopolitical reasons of a single country, unlike GPS, even if the United States has guaranteed it will continue to work in 2007
A multiuse system
The constellation of 30 satellites will be deployed in three orbits around the earth, 23000 kilometers above the earth’s surface. These orbits have been chosen to optimize their performance and assure a quality of service even in the event a satellite fails, as others will be able to pick up the slack.
The control of the constellation (adjusting orbits, synchronization of atomic clocks, configuration verifications) will be assured by three ground stations, two working all the time and the third as a backup (even if this later becomes a different link in the control chain).
Different channels will be used, with open services, accessible to all but without an integrity message. Commercial services that are more precise (less then 1 meter) with an integrity message and signal encryption, a channel for public service missions (emergency services, transport of hazardous materials, etc) requires dedicated hardware, and a SAR channel (Search and Rescue) for distress beacons.
Status
Galileo will offer a certain amount of compatibility with the GPS and Glonass systems, allowing the signals from different GNSS systems to be combined so that more precision and reliability is available. Numerous manufacturers of GPS receivers have already announced compatible chipsets for the two different GNSS systems.
Currently, only two test satellites are in orbit, Giove A, since December 2005 and the first to emit Galileo signals, and Giove B, launched on the 27th of April 2008, which is almost identical to the final satellites, allowing for the validation of the onboard atomic clocks and the quality of the transmission signals. A third backup satellite, Giove A2, is also planned.
If the measures tested on Giove B are satisfactory, the first satellites of the Galileo constellation could be put into orbit from 2010, with the launch calendar planned in groups of three. The European satellite positioning system must be functional by 2013.
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